1. Field of the Invention
The present invention relates to an internal combustion engine. The present invention relates particularly to an internal combustion engine having an improved exhaust port structure, and a method of manufacturing the same.
2. Description of the Background Art
Conventional motorcycles may include, for example, a sub-chamber in the middle of an exhaust pipe of an exhaust device connected to a four-cycle internal combustion engine (see Japanese Utility Model Registration Application Publication No. Hei 4-52992, for example). The sub-chamber is made of a metal plate or the like in the shape of a box or a case. The inside of the sub-chamber is hollow. The sub-chamber has a structure in which the hollow portion of the sub-chamber communicates with the exhaust pipe through a communication hole, which is provided in an appropriate location in the exhaust pipe.
With the volume of the exhaust pipe increased, the sub-chamber thus configured, for example, absorbs exhaust pulsation in the low rotary speed range of the internal combustion engine, and enhances the intake/exhaust efficiency by using the reflection waves of the exhaust pulsation.
In the structure of the motorcycle having the foregoing internal combustion engine, however, the provision of the sub-chamber makes the sub-chamber likely to interfere with parts around the location in which the sub-chamber is set, and hence imposes restriction on the layout of the parts. In addition, the conventional practice is to form the sub-chamber in the shape of a case from a metal plate or the like, as described above. This entails a problem that the production of the sub-chamber increases not only the number of parts but also the number of manufacturing steps because the production needs a bending process for the metal plate.
The present invention has been made in view of the foregoing situation. An object of the present invention is to provide an internal combustion engine having a sub-chamber function which: does not interfere with parts around its set location; imposes no restriction on the layout of the parts; and does not increase the number of parts or the number of manufacturing steps.
In addition, another object of the present invention is to provide a method of manufacturing the internal combustion engine having the sub-chamber function which imposes no restriction on the layout, and which does not increase the number of manufacturing steps.